This invention relates to a chuck for rotating a drill string.
To investigate geological structures, holes are drilled into the ground utilizing a drill string that carries a drill bit at one end. The drill string is made up of a number of drill rods threaded together with each of the drill rods typically being in the order of ten feet in length. In conventional drilling, a drill rig is employed which allows the rods of the drill string to be assembled end to end and provides for the rotation of the drill string. Rotation is imparted to the rods by a drill chuck that engages the outer surface of one of the rods and transmits torque to the rod from the drive unit. The position of the chuck on the rod must be adjustable so that as the string penetrates the ground the chuck can be released, moved along the rod, and reengaged.
In conventional drill rod chucks, the jaws of the chucks are moved to a closed position gripping the drill rod under the force of large a number of preloaded coiled springs or Belleville washers. An hydraulically actuated operator is utilized to compress the coiled springs or Belleville washers to thereby release the jaws from their closed drill rod gripping position and to open them for advance of the drill rod therethrough.
To provide adequate drill gripping force to rotate the drill string in the case of the coiled springs, a large number of springs are required, e.g. some 22 coiled springs, which have a significant height of 8 to 12 inches. Again, with the Belleville washers, a large number of stacks of washers, e.g. 18 stacks, of heights comparable to the coiled springs are required.
To accommodate the large number of springs or washer stacks conventional chucks are necessarily large, heavy and costly.
One of the problems with conventional chucks is that, in use over time, the initial force imparted by the coiled springs or Belleville washers deteriorates reducing the grip and hence the positiveness of the drive to the drill rod. Moreover, such deterioration is nonuniform from spring to spring so that the grip of the chuck jaws is not uniform around the rod.
Further, the force exerted by the coil springs or the Belleville washers is inherently less when they are extended so that in time worn drill rods may even slip through the chuck.
It will be understood that in order to provide the required chuck closing force, the springs or washers must be preloaded when assembled into the chuck so that they are under compressive force between a fixed surface or pressure pad and the jaw actuator. As a result, the chuck has a dangerous potential to fly apart and cause serious injury, for instance, when a retaining bolt is removed or bolt threads are stripped.
Again, in conventional chucks the bearing between the axially moveable non-rotating hydraulic operator and the chuck actuator is maintained in contact with the chuck actuator with the chuck in the closed position and driving the drill string from the drill rotation or drive unit. This results in generating very significant heat during the drilling operation. This heat added to the heat generated by the chuck driving unit renders their surfaces dangerous to the operator and capable of causing serious burns.
A further problem with conventional chucks is that, not only are the coiled springs or Belleville washers inherently subject to different rates of loss of resiliency or compressive forces as mentioned above, but they operate in an environment where they are subject to deterioration through corrosive damage due to contact with water and sludge shortening useful spring and washer life.
A still further problem with conventional chucks is that the jaws are not adequaately supported against the high cantilever and twisting forces causing loss of grip, eccentricity, run out virations, and jamming.
It is the object of the present invention to overcome the above disadvantages as well as others of conventional chucks as will hereinafter appear.
One important aspect of the present invention resides in eliminating the use of mechanical springs or washers with their inherent limitations and instead utilizes compressed gas to provide the force to close the chuck jaws to grip the drill rod.
With the utilization of compressed gas to provide the force to close the jaws of the chuck on a drill rod of a drill string, it has been found that the closing pressure can be both accurately set yet altered as desired. Further, the jaws can be moved uniformly to close on the drill rod to provide a balanced or uniform grip around the rod while maintaining an essentially constant gripping force throughout the jaw travel. As a result, the jaws can grip rods of different diameters with essentially equal and sufficient force not only to provide the requisite torque transfer regardless of such variations in drill rod diameters.
More particularly, in keeping with this aspect of the invention, the chuck actuator which moves axially longitudinally of the spindle to open and close the jaws is operated in the jaw closing direction by a source of compressed gas in the form of a plurality of compressed gas springs disposed symmetrically around the chuck actuator and acting between the jaw actuator and a suitable stop surface or pressure pad fixed to the spindle.
Compressed gas springs are commercially available and comprise cylinders into which compressed gas, eg. nitrogen, is introduced. The compressed gas forces a slideable small diameter cylindrical plunger or piston outwardly to a maximum position. Under the application of a force on the outer end of the plunger, the plunger can be displaced telescopically back into the cylinder against the force of the contained compressed gas. The travel of the plunger from its point of maximum projection to its point where it is fully retracted is the stroke of the plunger. Such gas springs using compressed nitrogen gas are sold, for example, by Hyson Products. These gas springs are extremely compact and provide much more force in a very much smaller area than conventional mechanical springs. For instance, a nitrogen gas spring having a diameter of 2xc2xe inches can provide the same force as from 8 to 10 coiled springs having a diameter of 2 inches.
In the case of coiled springs, for optimum life the springs should not be deflected more than 25% of their total length. Therefore, in the case of an application requiring a 3 inch stroke, the height of the spring should be 12 inches.
For a corresponding 3 inch stroke, the height of a gas spring is almost half that of the coiled spring.
It will be understood that on contact with the plunger of a gas spring the full force of the compressed gas in the cylinder is available to resist inward movement of the plunger whereas in a coiled spring, unless it is preloaded, there is no force on simple contact with the spring. Moreover, gas springs provide a nearly constant force resisting inward movement throughout the stroke of the plunger.
In addition, as the compressed gas within the cylinder of the gas spring is trapped from escaping, unlike coiled springs or washers whose force deteriorates with age and use, the force exerted by the gas spring remains constant with time and regardless of the frequency of its use. On the other hand, the force of the spring can be altered as desired by introducing a measured amount of compressed gas, eg. nitrogen gas, into the cylinder or exhausting a measured amount if desired. Thus, each spring can be calibrated to provide a precise spring force so that a number of identical gas springs having precisely the same spring force and other characteristics can be provided.
The jaws are moved by a jaw actuator in the form of a bowl or ring which cooperates with the jaws which are arranged at equally spaced intervals symmetrically around the spindle in a circular configuration. The jaw actuator or bowl opens the jaws as it is moved upwardly under hydraulic force and closes the jaws as it is moved downwardly under the force of a highly efficient compact arrangement of gas springs.
More particularly, according to the preferred form of the invention utilizing gas springs, the gas spring arrangement comprises a series of individual equally spaced gas springs arranged in a circle around the actuator bowl between the chuck jaws with the cylinders of the springs embedded in the upper end of the actuator and their plungers or pistons engaging a fixed surface or pressure pad secured to the end of the spindle.
This arrangement results in an extremely compact chuck and with the gas springs which have identical strokes charged with the same gas pressure selected to give the desired jaw force, the chuck is precisely balanced to provide a uniform gripping force around the drill rod. Moreover, this gripping force remains essentially constant for different drill rod sizes.
Another important aspect of the invention resides in the support system for the chuck jaws to prevent their displacement under the cantilever loads generated during the drilling operation.
According to this aspect of the invention, the jaws are held from rocking by a set of bushings selected for the size of the drill rod to be driven. Each bushing set comprises a lower bushing supported within the spindle beneath the bottom of the jaws and an upper bushing mounted to extend into the spindle to overlie the top of the jaws, the arrangement being such that the jaws can slide radially in and out of rod gripping and rod releasing positions but are prevented from tipping either up or down.
To provide positive open and closing jaw movement under sliding movement of the ring actuator, according to the preferred form of the invention, the rear edges of the jaws are beveled outwardly from their upper end to their lower end preferably at an angle of 15 degrees and are provided with similarly slanted key ways in their side faces adjacent their rear edges. The actuator in turn is provided with correspondingly slanted or beveled slots to receive the rear edges of the jaws with the side walls of the slots having projecting ribs or keys to engage in the jaw key ways. The walls of the slots themselves engage the sides of the jaws to preclude their twisting.
Because the jaws and actuator ring rotate with the spindle while the hydraulic operator does not rotate, a ball thrust bearing is interposed between the hydraulic operator and the actuator.
Another aspect of the present invention is the provision for the hydraulic operator to withdraw the thrust bearing out of contact with the actuator with the jaws closed to eliminate the intense heat at the bearing which occurs in conventional chucks during drill string rotation. As a result, the bearing is cool and can be serviced if required during the drilling operations.
Further, in this connection, the invention provides for a labyrinth seal between the hydraulic operator and the jaw actuator to prevent the expulsion of jaw lubricant or the ingress of water.
With this sealing arrangement containing outflow loss of lubricant, the invention also provides a jaw lubricating system which not only provides for lubrication of the jaws by also provides for lubricant flow between the jaws so that all jaws are properly lubricated at all times.
To ensure accurate relative positioning of the spindle actuator and other components at all times the invention also provides a guide pin arrangement which prevents jamming of the jaws so that they can easily be removed and replaced in the actuator bowl and to ensure that there is no misalignment of the springs.
Again, according to a preferred form of the invention provision is made to block any water flow entering the jaws from flowing down the spindle and discharging it out of the chuck by centrifugal force.
In still another aspect of the invention, the carbide grippers in the jaws utilize an angled tooth pattern which increases the gripping strength of the jaws since each tooth has a separate xe2x80x9cplowxe2x80x9d path through the rod material. If the teeth are in-line, grip failure will occur when the material around each tooth deforms to the point where only the first tooth is in contact with parent rod material.